Banking Details Still Not Updated

I've been banking with Nedbank for 2 Years. This year around June I changed to FNB so I've decided to call Telkom to have my banking details changed from Nedbank to FNB. It's now 7 Months I've even closed the Nedbank account but Telkom is still debiting that account and not my FNB account resulting in a Bounced Debit order, Added fees for a bounced debit order. Each time I call the callcentre they say the banking details that are showing on their side is FNB and I'm priomised that I will be debited from FNB at the end of the month it's been 7months with this.... It's really frustrating, Can somebody please help me